Padparadscha or Pretender • An Unusual Pink-Orange Sapphire

An orangish pink “padparadscha” sapphire was submitted for testing at Lotus Gemology’s Bangkok laboratory. Testing showed a number of conflicting features that suggested the gem was a cleverly treated synthetic pink sapphire designed to imitate natural padparadscha.

Introduction

In November of 2015, an orangish pink “padparadscha” sapphire of 14 ct was submitted for testing at Lotus Gemology’s Bangkok laboratory. At the time of take-in, the client stated that the gem’s origin was Sri Lanka, but the client was unsure of whether or not it had been treated.

Testing showed a number of conflicting features. Large fissures across the stone were filled with unusual orange stains displaying dendrite inclusions, along with needles along twin planes and what appeared to be tiny gas bubbles. Chemical analysis was performed by the Asian Institute of Gemological Sciences’ Bangkok lab. The lack of gallium and other features suggested this was a cleverly treated melt-grown synthetic pink sapphire designed to imitate padparadscha.

Figure 1. The 14-ct sapphire that is the subject of this report. Photo: Wimon Manorotkul/Lotus Gemology. Click on the photo for a larger image.

Figure 2. The same stone viewed from the back. One can clearly see the orange color in the fissure, with the pink color from the stone’s body. Photo: Wimon Manorotkul/Lotus Gemology. Click on the photo for a larger image.

General properties

Standard gemological testing revealed properties that were typical for corundum, with one exception. The typical ultraviolet fluorescence for padparadscha sapphires ranges from orange to red in both long wave (LW) and short wave (SW), with LW being stronger than SW. However this stone suspiciously showed SW fluorescence equal to that of LW.

Microscopic features

Microscopic examination provided further clues to the stone’s identity. The most prominent internal feature was a large orange-stained fissure extending across half the stone (Figure 1). This added an orange color in the otherwise pink stone, superficially causing it to resemble a padparadscha sapphire.

The filling material was also quite unusual, featuring black dendritic inclusions and a glassy surface sheen at certain angles that resembled the filling of lead glass filled rubies and sapphires (Figures 3–5).

Figure 3. This large orange fissure was the major feature of an otherwise pink sapphire. Photo: E. Billie Hughes/Lotus Gemology. Click on the photo for a larger image.

Figure 4. Another view of the filled fissure with its black dendrite inclusions. Photo: Richard W. Hughes/Lotus Gemology. Click on the photo for a larger image.

Figure 5. Under magnification, the large fissure displayed a number of unusual features, including black dendrites and a reflective sheen somewhat akin to that seen in glass-filled corundums. Photo: E. Billie Hughes/Lotus Gemology. Click on the photo for a larger image.

Further examination revealed dislocation needles along twin planes (Figure 6). While such needles are typical of natural corundum, on rare occasions they have been seen in synthetic corundums (Eppler, 1964; Hughes, 1997). Immersion between crossed polars revealed Plato-Sandmeier twinning (Figure 7).

Figure 6. Parallel dislocation needles were seen in a single twin plane just above the fissure. Photo: E. Billie Hughes/Lotus Gemology. Click on the photo for a larger image.

More disconcerting was the discovery of two tiny pinpoint inclusions in the pink portion of the stone. These were extremely small, but looked identical to the gas bubbles that are a common feature of melt-grown (Verneuil, Czochralski) synthetic corundums.

Figure 7. When immersed in di-iodomethane (methylene iodide), the extent of the fissure becomes readily apparent. Adding polarized light reveals Plato-Sandmeier twinning. A dislocation needle can also be seen at the lower center of the stone. Photo: Richard W. Hughes/Lotus Gemology. Click on the photo for a larger image.

Advanced testing methods

Non-destructive chemical analysis

The chemical analysis by ED-XRF (Energy-Dispersive X-Ray Fluorescence-Spectrometry) was performed using a Skyray Instrument EDX-6000B spectrometer with rotating table and spin option at AIGS in Bangkok. Full quantitative ED-XRF data with low error rates, high precision and good repeatability are achieved by calibration-curves using certified gem standards. Three different positions were analyzed, with the results given in Table 1.

Figure 8. ED-XRF spectrum (45KV) of the fissure revealed unusually high levels of lead (Pb) and copper (Cu).Click on the photo for a larger image.

Gallium (Ga2O3), which is typically found in all natural corundum, is completely absent; this suggests the stone is of synthetic origin.

Chromium shows up in concentrations from 340 to 410 ppm (0.035 to 0.041% Cr2O3). This produces the pink color.

Two elements of significance were also found in the fissure, as follows:

While lead was found in tiny amounts (10 ppm; 0.001% Pb) in the non-fracture area, high concentrations of more than 10,000 ppm (1.027% Pb) were seen in the fissure, suggesting it had been filled with lead glass (see Figure 7). Pb-rich glass is commonly used for clarity enhancement of rubies and sapphires (McClure & Smith et al., 2006; Choudhary, 2014; Leelawatanasuk & Susawee et al., 2015).

Surprisingly, copper was also found in the fissure. We suspect the copper unmixed to form the black dendrites. Artificially created dendrites have also been described in the literature (Fischer, 1991; Johnson & Koivula et al., 2000).

Tungsten (W), platinum (Pt) and gold (Au) are automatically analyzed in corundum measurement routines as well, as they might indicate a synthetic stone made by a crucible growth production (flux, hydrothermal). In this stone, no traces of these metals were detected. Iridium, which is commonly used as a crucible container in the Czochralski process, was also not detected. The presence of low concentrations of chlorine (Cl), potassium (K) and calcium (Ca) in the fissure appear to be components of the glass filler.

According to Muhlmeister & Fritsch et al.’s groundbreaking article on trace element analysis of ruby (Muhlmeister & Fritsch et al., 1998), “…the presence of Mo, La, W, Pt, Pb or Bi proves that a ruby is synthetic. Ni and Cu suggest synthetic origin…”. While they add the caveat that Ni and Cu could be present in sulfide inclusions in natural rubies, their research strongly suggests that the presence of Pb and Cu by themselves build a strong case for synthetic origin. Adding to this the complete absence of Ga and the conclusion is inescapable: this stone is of synthetic origin.

Infrared spectroscopy

The sample’s mid-infrared spectra (Figure 9), showed a series of bands at 2854 cm-1, 2923 cm-1 and 2958 cm-1. These bands are due to oil or grease from human fingerprints. The fuzzy and complex bands in the 3500-4000 cm-1 region, and the sharp peak at 2354 cm-1 resulted from the atmospheric fluctuations such as moisture and CO2 during the measurement. However, there was an absence of absorption bands related to the hydroxyl group or any hydrous minerals as previously reported in both natural and synthetic sapphires (Volynets & Vorob’ev et al., 1969; Moon and Phillips, 1994; Smith, 1995; Balmer & Leelawatanasuk et al., 2006; Beran & Rossman, 2006; Smith & van der Bogert, 2006).

Figure 9. This representative infrared absorption spectrum displays the series of bands due to oil or grease contamination (2800-3000 cm-1), and the atmospheric CO2 band at 2354 cm-1. FTIR spectrum was recorded in absorbance mode using a Thermo Nicolet iS50 FTIR spectrometer in the range 4000–400 cm-1, with a resolution of 4.0 cm-1 and 20 scans. Spectrum: Chawalit Chankhantha/AIGS. Click on the photo for a larger image.

Conclusions

Decades of testing precious stones in the lab have driven home many key lessons. But perhaps none is more important than that of the need to exercise great caution when confronted with a gem that presents contradictory evidence.

The late, great B.W. Anderson once wrote that the most common testing mistake by gemologists was a failure to consider enough possibilities. This was certainly true with this “padparadscha.” A hurried look would reveal the orange stains and dendrites in the fissure, and the dislocation needles and twinning would reinforce the view that this was a natural stone. Indeed, some of the junior gemologists who examined it first believed it to be genuine.

But the patient gemologist would reserve judgment, taking note of the unusual UV fluorescence (why is SW equal to LW?), the two tiny pinpoint inclusions (gas bubbles or crystals?) and the twinning (natural or Plato-Sandmeier type?).

Further testing would reveal trace-element chemistry in the pink portion of the stone that lacked gallium. In contrast, significant quantities of Pb and Cu were found in the fissure, with the Cu possibly unmixing as dendrites.

The result of the full collection of data is unmistakable—a “padparadscha” unmasked as a cleverly crafted pretender—a Verneuil melt-grown synthetic pink sapphire that had been artificially fractured and then had the fissure filled with a Pb-rich glass with traces of Cu.

About the authors

E. Billie Hughes is a 2011 graduate of UCLA, who obtained her FGA in 2013. A travel-addicted citizen of the world, Billie was born into a gem-loving family, with her first visits to gem mines at age two; by age four, she was mining sapphire in Montana. Since then, Billie has participated in gemological expeditions around the globe, including Burma, Sri Lanka, Thailand, Cambodia, Vietnam, Laos, India, China (Inner Mongolia & Tibet), Madagascar, Mozambique, Tanzania, Malawi, and Rwanda. Her work has appeared in books ranging from Terra Spinel, toRuby & Sapphire: A Collector's Guide, and Ruby & Sapphire: A Gemologist's Guide and publications including the Wall Street Journal, Gems & Gemology, InColor, The Gemguide, The Australian Gemmologist, and The Journal of the Gemmological Association of Hong Kong. Billie is an avid photomicrographer who was awarded first and second prizes in the Gem-A's 2016 Photographer of the Year competition, and second and third prizes in the 2014 competition.

Chawalit Chankhantha was at the time of publication working in the Bangkok lab of the Asian Institute of Gemological Sciences.

Dr. Andreas Burkhardt is one of the world's foremost authorities on ED-XRF and the President of Xray Analytics in Zürich, Switzerland.

Wimon Manorotkul is a gemologist with over 30 years' experience in the gem trade. A skilled photographer, her gem and inclusion photographs have graced numerous industry publications.